U.S. patent number 5,868,190 [Application Number 08/872,579] was granted by the patent office on 1999-02-09 for run-flat tire with an improved bead to rim interface.
This patent grant is currently assigned to Michelin Recherche et Technique, S.A.. Invention is credited to Jeffrey Scott Craddock, James Milo Endicott, Walter Lee Willard, Jr..
United States Patent |
5,868,190 |
Willard, Jr. , et
al. |
February 9, 1999 |
Run-flat tire with an improved bead to rim interface
Abstract
The run-flat tire has a tread for contacting a ground surface
and a belt package with belt plies interior to the tread for
support of the tread. A plurality of radially reinforced carcass
layers are positioned interior to the belt plies and include at
least one carcass layer that extends between spaced apart annular
beads. The tire has a pair of sidewalls each extending radially
inward from shoulders at lateral edges of the belt package to the
annular beads. The sidewalls have a plurality of sidewall
stiffening members to support the tire during a loss of inflation
pressure. The carcass layers are disposed with the sidewall
stiffening members to help support the run-flat tire with a loss of
inflation pressure. The spaced apart beads have a unique design
including bead cores placed at a predetermined diameter with
respect to a rim diameter, dual bead fillers above the bead cores,
a heel corner spaced at a radial gap distance from a rim flange and
rim interface components having a seat interface distance below the
bead core for mounting the run-flat tire on a conventional rim and
for sustaining the run-flat tire on the conventional rim with a
loss of inflation pressure within the run-flat tire.
Inventors: |
Willard, Jr.; Walter Lee
(Greenville, SC), Endicott; James Milo (Greenville, SC),
Craddock; Jeffrey Scott (Simpsonville, SC) |
Assignee: |
Michelin Recherche et Technique,
S.A. (CH)
|
Family
ID: |
25359887 |
Appl.
No.: |
08/872,579 |
Filed: |
June 10, 1997 |
Current U.S.
Class: |
152/517; 152/539;
152/552; 152/550; 152/540; 152/543; 152/544; 152/547; 152/541 |
Current CPC
Class: |
B60C
15/0607 (20130101); B60C 15/024 (20130101); B60C
15/06 (20130101); B60C 17/00 (20130101); B60C
15/0072 (20130101); B60C 15/04 (20130101); B60C
15/0018 (20130101); Y10T 152/10819 (20150115); Y10T
152/10828 (20150115); Y10T 152/10846 (20150115) |
Current International
Class: |
B60C
17/00 (20060101); B60C 15/024 (20060101); B60C
15/00 (20060101); B60C 15/06 (20060101); B60C
15/04 (20060101); B60C 015/00 (); B60C 015/04 ();
B60C 015/06 (); B60C 017/00 () |
Field of
Search: |
;152/517,539,540,541,543,544,547,550,552,555 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Abstract of JP-A-5-178037, 20 Jul. 1993, Japan (Ohtsu Tire &
Rubber Co Ltd). .
Abstract of JP-A-2-179513, 12 Jul. 1990, Japan (Yokohama Rubber Co
Ltd). .
Tire and Rim Association, Inc. Handbook 1997, 8-04 to
8-09..
|
Primary Examiner: Johnstone; Adrienne
Attorney, Agent or Firm: Csontos; Alan A. Reed; Robert
R.
Claims
What is claimed is:
1. A radial run-flat tire comprising:
a pair of sidewall portions;
a plurality of crescent shaped sidewall members in each sidewall
portion for supporting said tire with a loss of inflation
pressure;
a pair of spaced apart annular beads;
a pair of radially reinforced carcass layers extending from bead to
bead and disposed about said crescent shaped sidewall members;
a middle carcass layer extending from bead to bead between crescent
shaped members and having both ends partially encircling a
respective bead core and turned-up around said bead core to lap
with an outermost one of said pair of carcass layers; and
first and second bead fillers each disposed radially outward of
each bead core and axially between carcass layers, said first bead
filler extending radially outward from said bead core to form one
sidewall member of said plurality of crescent shaped sidewall
members and said second bead filler bounded by said first bead
filler and said bead core for providing a filler material adjacent
the bead core with a lower hardness than that of the first bead
filler.
2. The run-flat tire of claim 1 further comprising:
a bead core within each one of said beads having an annular coil of
wire or synthetic filaments generally forming a polygonal shaped
cross section with a predetermined tensile strength, said bead core
having an imaginary flat innermost surface defined by an imaginary
plane contacting said filaments, said innermost surface forming an
internal diameter of said bead core.
3. The run-flat tire of claim 2 wherein said tensile strength of
said bead core is defined by a tensile strength at one percent unit
strain with a value in a range of about 1100 Newtons per square
millimeter to about 3000 Newtons per square millimeter.
4. The run-flat tire of claim 3 wherein a torsional rigidity of the
bead core is at least 100 Newton meters per radian.
5. The run-flat tire of claim 4 wherein said torsional rigidity of
the bead core is about 200 Newton meters per radian.
6. The run-flat tire of claim 3 wherein a torsional moment of
inertia of the cross-sectional area of said bead core is in a range
of about 150 millimeters to the fourth power to about 350
millimeters to the fourth power.
7. The run-flat tire of claim 6 wherein the torsional moment of
inertia of the bead core is about 200 millimeters to the fourth
power.
8. The run-flat tire of claim 1 further comprising:
a plurality of elastomeric interface component portions in each
bead including a toe portion, a rim seat portion and a heel flange
portion forming a single component and having a predetermined
hardness and elastic properties for interfacing with a conventional
rim for the tire when mounted thereupon, wherein said heel flange
portion has a heel corner with a radial gap distance from a rim
flange when said run-flat tire is mounted on said rim and inflated
to its conventional inflation pressure.
9. The run-flat tire of claim 8 wherein said predetermined hardness
of said elastomeric interface component portions have a Shore A
hardness value in a range of about 50 to about 80.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to radial pneumatic tires used for vehicles,
and more particular to the design of the lower sidewall and bead
area of a run-flat tire to reduce the effort in mounting the tire
on a standard rim and to improve the retention of the tire on the
standard rim during a loss of inflation pressure.
2. Description of the Art
The need to carry a spare tire in a vehicle to replace a flat tire,
or more basically the need for a vehicle operator to stop and
replace a deflated tire at an inconvenient location, has long been
a concern of the vehicle operator. Many of these concerns can be
addressed with the use of a run-flat tire for allowing the operator
to reach a safe place or a service station before replacing a tire
which has lost its inflation pressure.
One of the problems associated with providing a run-flat tire is to
maintain acceptable performance of the run-flat tire upon
deflation. Essential to solving this problem is to provide a
run-flat tire which stays on the rim and keeps the vehicle
supported so the vehicle may drive to a more convenient location to
repair or replace the tire. The tire is generally retained on the
rim by the inflation pressure in the tire during normal running of
the vehicle. Absence of this inflation pressure tends to cause the
tire to want to be disconnected from the rim. This is especially
true during lateral maneuvers of the vehicle. Solutions to this rim
unseating problem include providing a special rim having a hump or
a depression for engaging the run-flat tire having a corresponding
special bead design. Typical efforts to modify the tire/rim seat
interface profiles are disclosed in U.S. Pat. Nos.; 4,779,658;
5,263,526; and 5,427,166. However, the use of standard rims with
these special run-flat tires will not optimize the bead unseating
problem. In addition, the effort required to seat these special
run-flat tires on rims with special tire/rim interface designs is
excessive.
Part of the rim unseating and vehicle handling problems have been
solved by the use of sidewall reinforcing members in a run-flat
tire to provide laterally stiffened sidewalls. Typical run-flat
tires with reinforced sidewalls are disclosed in the three U.S.
Patents disclosed above as well as in U.S. Pat. Nos. 5,158,627;
5,368,082; and 5,511,599. The crescent shaped sidewall reinforcing
members are essential for holding the tread displaced from the rim
to make the tire respond to vehicle maneuvers with the loss of
inflation pressure in the run-flat tire. Tires with sidewall
reinforcing members are used with the improved bead seat design of
this invention.
The heavy duty radial tire of U.S. Pat. No. 5,085,260 discloses a
smaller apex filler along with a number of carcass layers turned up
around the bead core. The length of carcass turn-up portions and
the position of the bead core in relation to the rim flange height
is used to obtain bead strength. Accuracy in the placement of end
points of each carcass layer is important in the teachings of this
1992 patent.
Changing the shape, dimensions and material properties of
components in the lower sidewall and bead of a tire can affect
their ability to resist higher forces and moments. The run-flat
tire can be designed to take advantage of changing shape,
dimensions and material properties. One component which can be
easily modified is the bead filler. A bead filler which has been
extended radially into the area of the sidewall in U.S. Pat. Nos.
4,640,329; 4,766,940; and 5,048,584. This extension provides
improved transverse and radial load supporting capabilities for the
tire. However, the material properties of the filler needs to be
different near the bead core than radially outward in the sidewall
to resist different loads in these different locations of the
run-flat tire and to facilitate an efficient tire fabrication
process. The disclosures of U.S. Pat. Nos. 4,046,183; 4,120,338;
and 4,508,153 and Japan Patent No. 5-178037 illustrate the use of
bead fillers having two parts; being one part adjacent a bead core
and another part extending into the sidewall area. These two-part
bead fillers use different size, shape and material properties for
each of the two parts. The bead fillers of these references also
require additional reinforcing layers placed adjacent to the bead
fillers to improve durability and strength of the bead region of
the tire. The need remains to simplify the use of two-part bead
fillers while maintaining their advantages.
Another design parameter which can be incorporated to transfer
loads from the vehicle to the ground by way of the run-flat tire is
the use of the rim flange. If a tire can be made to contact the
flange of the rim, the vehicle loads can transfer loads to the rim
at its flange. The rim flange contact is also useful in
transferring lateral loads between the tire and the rim that would
otherwise act to unseat the tire from the rim. Rim flange seating
of the tire is well known in the art as disclosed in U.S. Pat. Nos.
3,983,918; 4,203,481; and 5,033,524. Both U.S. Pat. No. 3,983,918
and U.S. Pat. No. 5,033,524 disclose the use of an additional
product in the tire to interface with the rim flange. A gap between
the rim and a buttress on the tire in U.S. Pat. No. 3,983,918 is
closed when the buttress contacts the rim flange. The tire to rim
flange contact is known to help with vehicle handling in some
maneuvers of the vehicle and to degrade the vehicle handling with
other maneuvers. It is important to know at what operating
condition the tire to rim flange can be used as an advantage. The
need remains to identify when contact of a run-flat tire with a rim
flange can be useful for the partially inflated run-flat tire.
A further problem exists with the pressure of the run-flat tire on
the rim seat portion of the tire to rim interface. A tire is
mounted on a rim with a combination of inflating and pushing the
tire to its proper place on the rim. The rubber in contact with the
rim must be durable and effective in sealing the interface against
loss of inflation pressure caused by air leaking out from inside
the tire. It is well known in the art to use an additional rubber
layer for making direct contact with the rim seat portion. In U.S.
Pat. No. 5,511,599 a rim seat ply is used to making contact with a
rim. Economy in manufacturing the run-flat tire can be realized by
a single bead interface rubber. The use of a single rubber
component for the bead interface rubber is disclosed in U.S. Pat.
Nos. 4,235,273; 4,790,364; and 5,033,524. The profile of the
innermost area of the bead interface rubber is also important for
providing desired pressures at the tire to rim interface. In U.S.
Pat. Nos. 4,554,960 and 5,464,051 a profile is disclosed for
providing a proper bead to rim interface seat area. The extent of a
single bead interface rubber which can also provide a rim flange
seat and a durable bead toe remains unsolved by these references.
The material properties of this bead interface rubber also remains
undefined.
Even with the improvements of the references the need remains to
have a lower sidewall and bead structure which has an improved bead
retention capability without compromising the ability to sustain
the same vehicle loads and without the necessity of added
reinforcing layers or other non-standard tire components. A
coexisting need is to be able to use run-flat tires on standard
rims that generally exist in the replacement market at the present
time. Both of these needs should be achieved while maintaining a
manufacturing process with limited changes and preferably lower
costs for the run-flat tire.
Accordingly, one object of this invention is to provide a run-flat
tire having annular beads designed so that the run-flat tire can be
easily mounted on a standard rim of a vehicle without excessive
over-pressures.
Another object of the present invention is to provide a run-flat
tire having annular beads designed to maintain a good seal between
the tire and the rim for maintaining an inflation pressure within
the tire.
Yet another object of the present invention is to provide a
run-flat tire having annular beads designed so that the run-flat
tire strongly resists being removed from the standard rim during
loss of inflation pressure.
A further object of the present invention is to simplify the design
of the bead area to reduce the number of different rubber
components used in the bead area when manufacturing the run-flat
tire.
Still another object of the present invention is to use materials
in the bead area which are resistant to damage when mounting the
run-flat tire on the standard rim and resistant to loss of air
between the tire and the rim during normal operation of the
run-flat tire on the vehicle.
SUMMARY OF THE INVENTION
The run-flat tire of this invention is easily mounted on a rim of a
vehicle for normal operation of the vehicle. The tire is useful for
many vehicles including passenger cars, light trucks, trucks and
the like. The tire has a tread portion for contacting a ground
surface and a belt package with belt plies interior to the tread
for support of the tread. A plurality of carcass layers positioned
interior to the belt plies extend between spaced apart annular
beads. The tire has a pair of sidewall portions each extending
radially inward from shoulders at lateral edge of the belt package
to the annular beads. The sidewalls have a plurality of sidewall
stiffening members to support the tire during a loss of inflation
pressure. The carcass layers are disposed with the sidewall
stiffening members to help support the run-flat tire with a loss of
inflation pressure. The spaced apart beads have a unique design
including bead cores placed at a predetermined diameter with
respect to a rim diameter, dual bead fillers above the bead cores,
a heel corner spaced at a radial gap distance from a rim flange and
rim interface components having a seat interface distance below the
bead core for mounting the run-flat tire on a conventional rim and
for sustaining the run-flat tire on the conventional rim.
In one embodiment of the present invention a radial pneumatic tire
is provided for mounting on a rim of a vehicle to sustain vehicle
loads by contacting a ground surface at a contact patch of said
tire when inflated and with a loss of inflation pressure. The tire
comprises a plurality of carcass layers disposed about sidewall
stiffening members for supporting vehicle loads with the loss of
inflation pressure. A pair of spaced apart annular beads are
interconnected by said carcass layers. Each one of the beads has a
bead core, a bead filler and rim interface components for mounting
and sustaining the tire on a conventional rim. The bead core has an
annular coil of wire filaments forming a polygonal cross-section
having a predetermined tensile strength and a flat innermost
surface defined by an imaginary plane contacting the filaments. The
bead core has an internal diameter, measured to said innermost
surface of the bead core when the tire is cured and the annular
beads are spaced apart an axial distance corresponding to a width
of the conventional rim on which the tire is to be mounted, which
is about 5 millimeters larger than a standard rim diameter of the
conventional rim. The rim interface components of the beads include
elastomeric portions being a toe portion, a rim seat portion and a
heel flange portion. The elastomeric portions have a predetermined
hardness values and modulus for interfacing with the conventional
rim. The heel flange portion of the rim interface components has a
heel corner radially spaced from a rim flange of said conventional
rim, over a substantial portion of a circumferential extent of said
heel flange portion, a radial gap distance when the tire is mounted
on the rim. The radial gap distance has a value in the range of
about 3 millimeters to about 8 millimeters when the tire has 100
percent of a conventional inflation pressure and a conventional
maximum tire loading from the vehicle loads. The radial gap
distance has a zero value adjacent the contact patch of the tire
during 100 percent of the conventional loading from the vehicle
loads with a reduced inflation pressure being less than about 15
percent of the conventional inflation pressure. The rim interface
components have a seat interface distance, measured radially
between the flat interface surface of a respective bead core and
the innermost surface of said rim seat portion at a lateral
centerline of the respective bead core of the tire after the tire
is cured, in a range of values of about 4 millimeters to about 6
millimeters. Wherein the tire is easily mounted on the conventional
rim and remains on the rim with the loss of inflation pressure.
In one embodiment the run-flat tire of this invention has a first
carcass layer positioned interior to the belt package which extends
from bead to bead and forming a carcass turn-up that partially
encompasses a respective bead core and extends radially outward to
an end point radially outward of a flange of the rim when the
run-flat tire is mounted on the rim. A second other carcass layer
extends from bead to bead and terminates at each end near to a
respective bead core to overlap with the turn-up portion. A third
carcass layer is also preferred which extends from bead to bead to
terminate at each end near a respective bead core. An innerliner
ply is positioned in the tire to the inside of the inner carcass
ply and forms the inner surface of the tire to help retain an
inflation pressure within the tire. Alternately, two of the carcass
layers can be discontinued in a central portion of the crown area
of the run-flat tire below belt package.
In another embodiment a first bead filler of each annular bead
extends radially outward of the bead core. A second bead filler is
placed radially inward of the first bead filler. The first bead
filler has a tapered cross-section with a decreasing thickness
outward of the second bead filler. The first bead filler extends
radially outward into the sidewall of the tire to provide a
sidewall stiffening member to help support the run-flat tire with a
loss of inflation pressure. The second bead filler extends a
relatively short distance radially outward from the bead core and
is made of a softer material than the first bead filler.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the present invention will become apparent to
those skilled in the art to which the present invention relates
from reading the following with reference to the accompanying
drawings, in which:
FIG. 1 is a cross-sectional view of one bead area of a run-flat
tire according to the prior art showing the tire mounted on a
special rim;
FIGS. 2 and 2A are cross-sectional views of one bead area of a
run-flat tire according to the invention and a standard rim showing
the relationship of the molded tire with respect to a standard rim
before being mounted on the rim;
FIG. 3 is a cross-section view of the run-flat tire of this
invention mounted on a standard rim and inflated, the tire being
symmetrical about a midcircumferential plane of the tire; and
FIG. 4 is a cross-sectional view of the run-flat tire of this
invention mounted on a standard rim in contact with a ground
surface and supporting a vehicle load with the loss of inflation
pressure, the tire being symmetrical with respect to a
midcircumferential plane.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The interface between each annular bead of a run-flat tire and the
rim of a vehicle using run-flat tires is critical to the safe and
efficient operation of the vehicle. The previous discussion
illustrates the importance of keeping the run-flat tire mounted on
the rim with a loss of inflation pressure. A typical run-flat tire
of the art is illustrated in FIG. 1. This run-flat tire has a
sidewall 61 with sidewall reinforcing members 60 which combine with
reinforced carcass layers 62, 64 and 68 to support the load of a
vehicle with a loss of inflation pressure in the run-flat tire.
Other run-flat tire designs are disclosed in the background section
of this invention and are known in the art which are similar to the
typical run-flat tire used herein. The run-flat tire of FIG. 1 has
the essential components of a run-flat tire to demonstrate the
improvements in the present invention.
A sidewall rubber 21 of the sidewall 61 typically covers the outer
surface of the tire and keeps the carcass layers and the
reinforcing members from damage, as illustrated in FIG. 1. The bead
area 20 has a number of components which provide support for the
loads being transferred to a rim 70 and for interfacing with the
rim. A bead filler 24 is provided which extends radially outward
from a bead core 22 and becomes one of the sidewall reinforcing
members. Inner and outer carcass layers 68 and 64 extend to
radially inward to end points 68a and 64a respectively near the
bead core. The middle carcass layer 62 partially wraps around the
bead core and forms a turn-up carcass layer 66 adjacent the bead
filler to provide a long lapp length with outer carcass layer 64.
Three different rubber components are used to the exterior of the
carcass layers in the bead area. A rim seat portion 26 is located
between a heal flange portion 29 and a toe portion 28. A reinforced
seat ply 27 interfaces with a special rim 70. The bead seat portion
adjacent the seat ply helps the seat ply to contact a curved area
and an outermost flat area 76 of the rim to develop a interface
pressure to hold the run-flat tire on the rim. The toe rubber 28
helps the seat ply to contact a special hump 72 on rim 70 at a hump
point 75 so that the run-flat tire remains seated on the rim with
the loss of inflation pressure. The heal flange rubber 29 helps
transfer loads into the sidewall of the run-flat tire with the loss
of inflation pressure. Additional components added to the lower
sidewall and bead area of a run-flat tire are known in the art to
improve bead seating an load supporting capabilities of the
run-flat tire. These additional components include but are not
limited to chafers, reinforced plies and the like. The extent and
number of different components in the bead lower sidewall and bead
area make the run-flat tire more complex to manufacture and less
economical to produce.
The run-flat tire of this invention is suited to be used on
conventional rims and has been simplified by using only a limited
number of components in the lower sidewall and bead area of the
run-flat tire. The size and shape of the present run-flat tire also
control the ability of run-flat tire to be mounted on the
conventional rim and to remain on the rim with a loss of inflation
pressure. The use of materials for the various components of the
bead area of the run-flat tire of this invention further enhance
its performance. The lower sidewall and bead area of a run-flat
tire 10 of this invention is illustrated in the cross-sectional
view of a single bead area in FIG. 2. The run-flat tire has been
molded to have a shape and size for mounting on a conventional rim
80.
Bead areas 30 for the run-flat tire of this invention have been
designed to work with a run-flat tire having sidewall stiffening
members 50, a pair of bead cores 32 and a plurality of carcass
layers 40. The run-flat tire illustrated has three sidewall
stiffening members including a first bead filler 34. Stiffening
members extending from the bead area radially outward into the
sidewall, to support loads on the rim from a ground surface when
the run-flat tire is mounted on the rim. There are three carcass
layers illustrated to including an inner carcass layer 48, a middle
carcass layer 42 and an outer carcass layer 44. The carcass layers
are disposed with the sidewall stiffening members is forming
run-flat tire 10. The carcass layers include a conventional rubber
matrix radially reinforced with conventional parallel reinforcing
members or synthetic cords which extend essentially radially; being
at an angle of less than about 15 degrees from a radial plane
containing the axis of rotation A of the run-flat tire, as shown by
the cross-section of FIG. 2. The sidewall supporting members are
made of rubber material having a high modulus and hardness
convention in the art. Other sidewall configurations are within the
scope of this invention including run-flat tires with one or two
sidewall stiffening members and two carcass layers.
In another embodiment of the invention each bead filler of this
invention is made in two parts to improve the manufacturing process
in obtaining a good bond with bead core 32. First bead filler 34
extends radially outward into the sidewall and provides one of the
sidewall stiffening members 50 on each lateral side of the run-flat
tire. A second bead filler 37 has a gum drop cross-sectional shape
and is placed radially outward of the bead core to provide a softer
material having a lower Modulus. The soft second bead filler
improves the manufacturing process when forming the tire into a
thyroidal shape. This lower modulus material of the second bead
filler also allows the bead core to conform better to the shape of
the rim when mounting the run-flat tire and when the tire is
running with the loss of inflation pressure. The first bead filler
is made to have a Shore A hardness with a value in the range of
about 70 to 90 and a Modulus of Elasticity at ten percent unit
strain with a value in the range of about 7 MegaPascals (MPa) to
about 15 MPa. The second bead filler 37 is made to have a Modulus
less than the Modulus of the first bead filler. The second bead
filler has a Modulus of Elasticity in tension at ten percent strain
with a value in a range of about 3 MPa to about 10 MPa.
The carcass layers of the run-flat tire of this invention are
truncated as they approach the bead core 32. One carcass layer
extends around the bead core and turns up to extend radially
outward toward sidewall 41. The inner carcass layer 48 is
illustrated in FIG. 2 to have a turn-up portion 46 that overlaps
with the outer carcass layer 44. The middle carcass layer 42 is
terminated as it laps with the outer carcass layer radially outward
of the bead core. Which carcass layers are terminated and which are
turned up around the bead core are not critical. However, the
configuration illustrated and described is the preferred
configuration for improved performance and for economy in
manufacturing the run-flat tire. Outer carcass layer 44 has been
terminated a distance C1 above a bead reference line R. The bead
reference is defined by an imaginary plane contacting filaments 32a
on the flat interior surface 33 of the bead core 32. Bead reference
R is parallel to the axis of rotation A of the run-flat tire. An
end point 44a of the outer carcass layer is terminal at the
distance C1 having a value in the range of about 10 millimeters to
about 30 millimeters. The middle carcass layer 42 is terminated at
an end point 42a which has a distance C2 radially outward of the
bead reference R. Distance C2 has a value in the range of about 15
millimeters to about 25 millimeters. Lap distances L1 and L2 are
necessary with carcass layer 48 before the carcass layers 42 and 44
can be terminated. Carcass layers 44 and 42 have a lap distances L1
and L2 respectively with a value in the range of about 10
millimeters to about 25 millimeters.
In a further embodiment the bead core 32 of the bead area 30 is
preferably made with a plurality of layers formed by an annular
coil of wire or synthetic cord filaments 32a nestled together, as
illustrated in FIG. 2. Each layer is made to be an equal distance
from the axis of rotation in this preferred embodiment. The
position of the bead core of a cured tire with respect to the rim
80 on which it is to be mounted is critical for mounting the
run-flat tire and keeping the tire seated on the rim with a loss of
inflation pressure within the run-flat tire. Flat interior surface
33 defined by reference line R is used to properly locate the bead
core of the cured tire. An internal bead core diameter TD is
measured to the reference line defining the flat interior surface.
The internal bead core diameter is measured when the tire is cured
and the beads 30 of the run-flat tire are spaced axially apart a
distance corresponding to a width of a conventional rim on which
said tire is to be mounted.
Defining a relationship between the internal bead diameter TD to a
conventional rim diameter RD establishes a critical design
parameter unique to the present invention. Conventional rims are
defined herein to refer to Standard Rim Contours defined in the
1997 Year Book of the Tire and Rim Association, Inc. of Copley,
Ohio on pages 8-04 to 8-09. The information of this reference is a
part of this disclosure by reference thereto. The internal bead
core diameter TD of the bead core 32 of the run-flat tire of this
invention is made about five millimeters larger than the rim
diameter RD of rim 80 on which the run-flat tire is to be
mounted.
Another embodiment of the present invention is the ability to
easily mount the run-flat tire on a rim. In combination with the
bead diameter to rim diameter relationship, the ability to easily
mount the run-flat tire on the rim and keep bead area 20 seated on
rim 80 with a loss of inflation pressure within the run-flat tire
is very important. This ability is partially controlled by the
amount and type of components to be located between the bead core
and the rim. These components are defined herein to include
elastomeric portions 31 as well as any rubber plies (including
carcass layers) which are radially inside flat interface surface 33
of the bead core. A seat interface distance T is defined to be a
distance measured radially between the flat interface surface and
an innermost surface point 35 of rim seat portion 31 along a
vertical centerline V through a respective bead core 32. Seat
interface distance T has a value in the range of about four
millimeters to about six millimeters. Preferably the seat interface
distance is made so that the rubber rim seat rubber portion
comprises more than 70 percent of interface distance T. Consistent
with the seat interface distance the rubber rim seat portion must
have a Shore A hardness and a Modulus which will provide an
interface pressure between the rim and the run-flat tire to keep
the tire is inflated and to keep the run-flat tire seated on the
rim when the tire is deflated. The rim seat portion is made of an
elastomeric material having a Shore A hardness value in the range
of about 50 to about 80 and a Modulus of Elasticity in tension at
10 percent unit strain with a value in a range of about 5
MegaPascals (MPa) to about 9 MPa.
Another design parameter is defined so that bead core 32 can
generally be considered as a non-extensible annular ring when
mounting the run-flat tire on the rim. However, some stretching of
the bead core does occur when the run-flat tire is mounted on the
rim and a circumferential change in length does result in a small
but important change in its internal diameter TD of the bead core.
To control these small but important changes the bead core is made
to have a tensile strength at one percent of unit strain of the
bead core with a value in the range of about 1100 to 3000 Newtons
per square millimeter. A torsional rigidity of the bead core is
also important in keeping the run-flat tire seated on the rim. The
torsional rigidity is discussed and defined in a later section.
In another embodiment rim interface components of each bead 30
include elastomeric portions 31 as well as any carcass layers or
other reinforcing layers which are wrapped around the bead core.
Rim interface components include any component that extends between
bead core 32 and a rim seat 86 as well as components which contact
a rim flange 84. Rim interface components include elastomeric
portions 31 being a toe portion 38, a rim seat portion 36 and a
heel flange portion 39. Elastomeric portions can be separately
applied portions when making the run-flat tire, but are preferably
combined to form a single unit construction in making the tire. The
toe portion extends radially on the axial inside of the run-flat
tire and laps with an innerliner rubber 49 to help retain air
within the run-flat tire.
The run-flat tire of FIG. 2 has been made to be mounted on the
conventional rim 80 as illustrated in FIG. 2A. A relationship
between the rim diameter RB and the diameter TD of the bead core,
measured to the innermost surface defined by the bead reference
line R, has been discussed. In general, the rim diameter is about
five millimeters smaller than the diameter of the bead core for all
run-flat tire sizes. As the run-flat tire is placed on the rim, the
tire is over-inflated as it is forced axially outward over a drop
center 82 and onto the rim. Rim seat portion 36 of elastomeric
portions 31 of the rim interface components of the run-flat tire
contact a rim seat 86 of the rim and the run-flat tire is seated.
The rim seat portion is compressed against rim seat 86 of rim 80 to
provide a seal to retain air in the tire. A rim flange 84 of the
rim does not contact the run-flat tire during this mounting
process, but is used as a fulcrum for using tools to help in
mounting the tire on the rim.
The tire mounted and inflated on a conventional rim is illustrated
in FIG. 3. The run-flat tire 10 of this invention is mounted on rim
seat 86 of rim 80 and inflated to a conventional inflation pressure
for use on a vehicle. The cross-sectional view of FIG. 3 shows only
half of the run-flat tire with the run-flat tire being symmetrical
with respect to a midcircumferential plane P of the run-flat tire.
An innerliner rubber 49 is provided on the inside surface for
maintaining air within the run-flat tire. The crown portion of the
tire includes a tread 12 having a tread surface 14 for contacting a
ground surface to support a vehicle by transferring vehicular loads
from the rim through the tire to the ground surface. The tread is
supported by a plurality of reinforced belt plies 80 in a band
around the tire interior to the tread. The belt plies extend
laterally over the crown of the tire from one shoulder 83 to the
other shoulder.
The run-flat tire of FIG. 3 further illustrates at least one
carcass layer 48 extending from one annular bead 30 to the other
annular bead. Other carcass layers 42 and 44 are preferably
terminated at ends 42b and 44b as they lap with the belt plies at
each shoulder 83. The carcass layers can all extend from bead to
bead within the scope of this invention. The carcass layers are
disposed with the sidewall stiffening members 50 extending from the
shoulder to the annular bead in each sidewall 40 of the run-flat
tire. Preferably two carcass layers 42 and 44 are terminated at
points 42a and 44a above the bead core 32 of each annular bead. The
sidewall stiffening members include crescent shaped members such as
crescent member 54. The first bead filler 34 also provides one of
the sidewall stiffening members in this embodiment of FIG. 3. Other
known arrangements of carcass layers and sidewall stiffening
members can be used within the scope of this invention. Once again,
the use of a second bead filler 37 having a material with more
flexibility than the first bead filler helps with both mounting the
run-flat tire on the rim and in the fabrication process.
The second bead filler 37 shown in FIG. 3 is smaller and softer
than the first bead filler 34 for providing advantages in forming a
green run-flat tire during the tire building process and during
mounting of the cured run-flat tire on a rim. In addition, the
performance of the run-flat tire can be improved during running of
the vehicle by the addition of the second bead filler. The second
filler has a preferred gum-drop shape in the embodiment shown. The
cross-sectional length and width of the second bead filler can vary
to enhance making the run-flat tire and its use with a vehicle. The
second bead filler is bounded by the first bead filler and the bead
core in the cured run-flat tire.
One advantage of the addition of the second bead filler radially
outward of each bead core 32 is realized during a conventional tire
building process. The second filler helps in forming a green tire
into a toroidal shape from a cylindrical shape during the tire
building process. The harder first bead fillers are initially
placed on a cylindrically shaped tire building drum axially
interior to respective bead cores. The softer second bead fillers
are placed radially outward of the respective bead cores. The green
tire is removed from the cylindrical tire building drum and formed
into a toroidal shape. During formation of the toroidal shape the
first filler is rotated around the stationary bead core to become
radially outward of the second filler and the bead core in each
bead area 30. The second filler is made to remain stationary around
the bead core as the first filler rotates. This tire building
process has the advantage of allowing the first bead filler to
easily rotate from an initial position to a rotated position.
Problems associated with an elongated or odd shaped bead core are
compensated by the second bead filler. In addition, odd shaped bead
cores of the art frequently have problems with voids adjacent the
bead core of a cured tire. Voids adjacent the bead core are
essentially eliminated by the addition of the second bead filler of
this invention.
Another advantage of the addition of a second bead filler in
accordance with this invention is realized when a cured run-flat
tire is being mounted on a rim. The flexibility of the softer
second bead filler allows the bead core to be more compliant with
the stiffened sidewalls of the run-flat tire. The bead core becomes
deformed or deflected from its annular ring shape as the run-flat
tire is being mounted. The bead core is restrained less by the
softer more resilient rubber of the second bead filler during
mounting, so that the forces and overpressures used to mount the
run-flat tire are reduced as a result of the second bead
filler.
Additional advantages of the addition of the second bead filler
illustrated in FIGS. 2, 3 and 4 are associated with the performance
of a vehicle having the run-flat tires of this invention. The
presence of the second bead filler will have an influence on the
ride comfort and handling of the vehicle. The shape and extent of
the second bead filler in the inflated run-flat tire is optimized
to improve ride comfort and handling. With the loss of inflation
pressure the run-flat tire deforms or deflects to support the
vehicle through the supporting sidewalls of the run-flat tire, as
illustrated in FIG. 4. The bead area along with the bead fillers
bend so that the run-flat tire best conforms to the shape of the
rim without displacing the bead core or greatly reducing the
seating pressures at the run-flat tire to rim interface. The
ability of the bead fillers to help the run flat tire conform to
the rim is enhanced by the addition of the second bead filler.
Bending of the bead area is more critical during lateral maneuvers
of the vehicle and cornering maneuvers by vehicle are improved by
the addition of a second bead filler.
Generally speaking, the overall design of the first and second bead
fillers along with the bead core results in an improved process for
making the run-flat tire, improved mounting of the run-flat tire on
a rim and improved driving performances of the vehicle when the
run-flat tire is inflated and with a loss of inflation
pressure.
A further embodiment of the invention is illustrated by the gap
distance G provided between rim flange 84 and a heel corner 31c of
elastomeric portions 31, as illustrated in FIG. 3. A gap distance
is known to be necessary for the inflated run-flat tire to respond
to vehicular maneuvers and maintain good vehicle handling and
cornering performance. An initial gap distance is provided for the
run-flat tire mounted on a conventional rim and inflated to a
conventional inflation pressure. Gap distance G has an initial
value in the range of about 3 millimeters to about 8 millimeters
depending on the size of the run-flat tire and the application rim
width. This initial gap distance begins to decrease as the run-flat
tire starts loosing inflation pressure.
The run-flat tire of this invention is made to have a predetermined
initial inflation pressure for seating the tire on the rim when the
run-flat tire is being mounted. The initial inflation pressure for
run-flat tire 10 has an average value in a range of about 30 pounds
per square inch (psi) to about 40 psi. The interfacing surfaces of
the tire's interface components 31 and rim seat 86 of the rim are
usually lubricated to reduce the effort in mounting the run-flat
tire on the rim. The toe point 85 of the bead is to become
positioned on the rim so that uninterrupted contact is made between
the run-flat tire and the rim when the run-flat tire is fully
mounted on the rim.
Inflating the mounted run-flat tire of this invention to a
conventional inflation pressure known in the art makes the run-flat
tire ready for use on a vehicle. Standard inflation pressures are
given in the 1997 Year Book of the Tire and Rim Association, as
previously referenced, for different tire sizes. The mounted and
inflated run-flat tire of this invention results in an average
interface pressure between the run-flat tire and the rim having a
value in a range of about 220 psi to about 365 psi. The preferred
average interface pressure for run-flat tire 10 on a passenger car
has a value of about 290 psi when the run-flat tire is inflated to
about 30 psi. The distribution of this pressure is controlled by
the run-flat tire of this invention so that no uninterrupted
contact is present at the interface between the run-flat tire and
the rim. This 290 psi pressure is referred to herein as the running
interface pressure. The running interface pressure of the run-flat
tire of this invention represents an increase of about 30 percent
to about 40 percent above that for conventional tires and rims of
the same size and loading capacity. The running interface pressure
is very important to ensure a tight seal for air retention within
the tire and to help ensure adequate zero inflation pressure seat
retention of the run-flat tire on the rim.
The run-flat tire of this invention running loaded with zero
inflation pressure and in contact with a ground surface is
illustrated in FIG. 4. This figure also shows a cross-sectional
view of only half of a run-flat tire 10 which is symmetrical about
the midcircumferential plane P. The Run-flat tire is mounted on rim
80 which is loaded by load L as the result of supporting the weight
of a vehicle. The rim interface components 31 of bead area 30
remain in contact with rim seat 86 and the toe point 85 remains at
the rim seat. The Bead core 32 has been able to keep the run-flat
tire on the rim and the bead fillers 34 and 37, along with the
other sidewall stiffening members 50 and carcass layers 40, have
deformed as a unit to support the vehicle. A ground surface 90
contacts tread surface 14 of the tread 12. Belt plies 80 supporting
the tread have a reverse curvature to transfer the loads on the
tread surface to each shoulder 83 of the run-flat tire. The
sidewall stiffening members and the carcass layers act as a
deformed beam to transfer loads to the rim with a loss of inflation
pressure.
An essential embodiment of the run-flat tire of this invention is
the contact of the tire with rim flange 84 of the rim, as
illustrated in FIG. 4. This contact between the heel flange portion
of the rim interface components 31 and the rim flange allows the
loads on the run-flat tire to be transferred directly to the rim
flange. Heel corner 31c is essential in loading the rim flange
without using the rim flange as a fulcrum to force bead core 32
away from bead seat 86. In other words, the load is transferred
from the run-flat tire directly to the rim flange without
introducing a prying action as the run-flat tire deforms with a
loss of inflation pressure. A corner angle CA at the heel corner is
measured by the angle made at the exterior surface as it bends
around heel corner 31c. The corner angle has a value of at least 30
degrees when the run-flat tire is cured (FIG. 2). The radial gap
distance G (FIG. 3) has been closed to zero. However, this occurs
before the inflation pressure has decreased to zero within the
run-flat tire. The heel flange portion 38 of the rim interface
components makes contact with rim flange 84 when the inflation
pressure becomes less than about 15 percent of the conventional
inflation pressure of the inflated run-flat tire. This unique
feature of the run-flat tire of this invention allows the tire to
be fully seated on the rim before the total loss of inflation
pressure; to insure the proper support of the run-flat tire by the
rim.
A further embodiment of the run-flat tire of this invention is
realized by defining the size, strength and flexibility of the bead
core 32. As illustrated in FIGS. 2-4, the bead core is a
fundamental structural component in the various stages of providing
a run-flat tire, mounting the tire and supporting the tire on a rim
during inflated and deflated conditions of the run-flat tire. The
tensile strength of the bead core is discussed above in relation to
mounting and retaining the run-flat tire on a conventional rim. The
ability of the bead core to resist being twisted is quantified by
its torsional rigidity. The torsional rigidity of the bead core 32
is very important, particularly when maintaining the run-flat tire
on the rim with a loss of inflation pressure. Torsional rigidity of
bead core 32 made of a annular coil of wire filaments is realized
by measuring the moment or torque required to rotate a 100
millimeter long test sample of the bead core through an angle of
2.5 degrees. The torsional rigidity of bead core 32 for the
run-flat tire of this invention should be at least 100 Newton
meters per radian and is preferably about 200 Newton meters per
radian. In addition, the torsional moment of inertial of the
cross-sectional area of the bead core is made to have a value in a
range of about 150 millimeters to the fourth power to about 350
millimeters to the fourth power, and preferably about 200
millimeters to the fourth power.
EXAMPLES
Sufficient bead retention capability of the run-flat tire of this
invention have been demonstrated when used on standard vehicles.
Both beads remained seated on the rim with zero inflation pressure
in the tire during all moderate and many severe maneuvers;
including the forty five mile per hour brake and turn maneuver used
in the industry as a standard for run-flat tire development. Many
of the industry standard maneuvers involve lateral acceleration
values in excess of 0.5 times the acceleration of gravity (0.5 Gs).
The run-flat tire of this invention exceeded all of the
requirements of these tests.
In very severe maneuvers, with standard vehicles going well beyond
standard test maneuvers, the run-flat tire with zero inflation
pressure remained on the rim with only the inner bead seated on the
rim seat. The retention of the run-flat tire seated on at least one
side of the rim enabled the vehicle to recover from a very severe
maneuver and still provided the vehicle with continued
mobility.
From the above description of preferred embodiment of the
invention, those skilled in the art will perceive improvements,
changes, and modifications. Such improvements, changes, and
modifications within the skill of the art are intended to be
covered by the appended claims.
* * * * *